"[The human being] has a character, which he himself creates, insofar as he is capable of perfecting himself according to ends that he himself adopts. By means of this the human being, as an animal endowed with the capacity of reason (animal rationabile), can make out of himself a rational animal (animal rationale)"
--- Anthropology from a pragmatic point of view / Immanuel Kant
"As Allen Wood notes: "Human beings are capable of directing their lives rationally, but it is not especially characteristic of them to exercise this capacity successfully. Rather, rationality must be viewed as a problem set for human beings by their nature”. In characterizing human beings’ relationship to rationality in this more qualified manner, Kant adds a further tentative note to his account of human nature. Humans are not inherently rational, but they have the capacity to become rational. And some of us may succeed more than others. Second, what Kant means by "rationa1ity" in this context is not instrumental rationality (choosing efficient means toward goals or ends that one desires) but substantive rationality (deliberating about and freely determining one’s ends). An animal that strategizes about how to satisfy its hunger exhibits instrumental rationality; an animal that reflects on and then renounces its hunger (say, in protest over an injustice) exhibits substantive rationality. Kant grants that animals have instrumental rationality—like humans, animals also act in accordance with representations (and are not, as Descartes would have it, machines)” (KU 5: 464n; cf. Politz 28: 274). Animals have desires, and many of them think about how to realize their desires. But Kant also holds that only humans—at least among the class of terrestrial beings—have substantive rationality: “in order to assign the human being his class in the system of animal nature, nothing remains for us than to say that he has a character, which he himself creates, insofar as he is capable of perfecting himself according to ends that he himself adopts” (Anrh 7 321). In emphasizing human beings’ capacity to pursue ends of their own choosing (substantive rationality), Kant adds yet another tentative note to his account of human nature. Because humans can freely choose their own ends rather than simply pursue the goals that they instinctively desire, their mode of life is radically indeterminate—open rather than fixed."
--- Kant's Human Being: Essays on His Theory of Human Nature / Robert B. Louden